1. Field of the Invention
The present invention relates generally to underwater dredging apparatuses and specifically to electrically powered cutter and suspension pump combinations.
2. Discussion of the Prior Art
Dredging systems generally mounted on floating barges have been in existence for many years. By means of an A-arm or ladder assembly, pivotally mounted on the front of the barge, a cutter head and suction tube are maintained in proximity to the bottom which is being dredged. The cutter head being powered by an electric or hydraulic motor has protrusions from it which scrape and otherwise disturb sand, mud and rocks on the bottom. The temporary suspension of bottom materials in the water resulting from the cutter head action is sucked through a suction tube and discharged away from the area of dredging in order that the solid materials may settle out and not fill in the area of dredging.
In typical dredging operations, the dredge is positioned over the area to be dredged and operations are commenced with the movement of the cutter head and suction device being controlled by movement of the entire barge itself. In some instances, the barge can be pivotally mounted for rotation about one end such that the dredging operations are commenced along an arcuate path spaced radially outward from the pivot point. However, it is necessary that the pivot point be changed in order to dredge the next subsequent arcuate path when clearing a channel or similar extended area. Thus, dredging operations are characterized by the need to constantly reposition the barge in order to progress in the dredging operations.
In several newer types of dredging apparatuses, a submersible electric motor powers a high volume impeller pump for sucking and propelling suspended particles of bottom material through a discharge pipe to a location some distance away from the dredging operations. In such prior art devices, two cutter head assemblies were generally mounted parallel with each other and the electric motor and pump assembly combination was suspended above and between the two cutter head assemblies. It was well-known that two cutter head assemblies were necessary. The cutter heads were rotated in opposite directions in order to prevent the torque from one cutter head assembly from rotating the entire cutter head/pump unit. Additionally, it was thought that the location of the pump inlet above the cutter head provided the optimum location for ingestion of suspended bottom matter disturbed by the cutter head assembly.
The cutter head assemblies generally comprised an electric or hydraulic motor powering a rotating shaft which has a cutter head located on the end. Typically, a cutter head as shown in FIG. 3 comprises an input shaft 10 which is connected to the electric motor at one end and to the cutter head assembly 12 at the other end. A generally conical shell section 14 has a plurality of teeth 16 extending therefrom. As the conical shell section rotates under the influence of drive shaft 10, in proximity to the bottom material, teeth 16 abrade and dig up the bottom material. The sand and silt bottom material is forced into suspension in the water thus facilitating the ingestion of the suspension into the pump and transport to the discharge pipe some distance away from the dredging area.
A typical electric motor/pump assembly is illustrated in FIG. 5 which shows the electric motor 20 and the impeller pump unit 22. Specifically, the electric motor is contained within housing 24 and powered by suitable sealed electrical power line 26. A drive shaft 28 connects the electric motor to the pump impeller 30 contained within pump housing 32. Supporting drive shaft 28 is bearing 34 which serves to position and locate the drive shaft/impeller assembly. It can be appreciated that the environment in the vicinity of impeller 30 will be quite abrasive with sand, mud and rocks suspended in water which is being pumped through the pump at extremely high rates of flow. Typically, multiple shaft seals 36 of elastomeric material are used to prevent the flow of the abrasive suspension from reaching bearing 34 whose replacement generally requires complete disassembly of the apparatus. FIG. 6 is a more detailed section view of the seal portion of prior art pumps.
As shown in FIG. 6, it is conventional to utilize a shaft collar 40 mounted for rotation on drive shaft 28. Multiple shaft seals 36 do not rotate and are fitted into a portion of the pump housing 32. Each seal generally comprises an elastomer portion 42 which has a lip 44 extending therefrom. The elastomeric lips of the various seals are maintained in place by suitable metal compression rings or spirals indicated at 46. Because there is relative rotation between the seal lips 44 and the shaft collar 40, it has been found that a great deal of wear occurs along shaft collar 40 necessitating its frequent replacement during dredging operations. Generally, the seals not only prevent the abrasive suspension from reaching bearing 34 but also prevent oil utilized for lubricating bearing 34 from leaking out into the impeller portion of the pump and thus contaminating the area in which dredging operations are being undertaken. The high wear rates of shaft collars 40 and seals 36 due to the suspension and oil mixture which occurs at one or more of the seals is the primary cause for the frequent repair and replacement of these items, resulting in substantial "down" time for the dredging operation.
In many locations of the country it is necessary to conduct dredging areas adjacent a road or other body of land where there is insufficient water to float a typical dredging barge. This generally precludes the use of a cutter head/pump combination for such dredging operations. Examples of such operations might be irrigation canals, drainage ditches, etc.
Because of the necessity to move the traditional foating barge everytime a new sweep is to be done, it is very difficult to have more than one barge conducting dredging operations at a time. Accordingly, dredging operations may take extremely long periods of time because of the requirement that only a single dredging barge can be utilized. Because of the "down" time associated with the above-mentioned seal wear problems, this dredging time is made even longer.